fetus - an unborn or unhatched vertebrate in the later stages of development showing the main recognizable features of the mature animalteras, monster - (medicine) a grossly malformed and usually nonviable fetus abortus - a human fetus whose weight is less than 0.5 kilogram when removed or expelled from the mother's body craniate, vertebrate - animals having a bony or cartilaginous skeleton with a segmented spinal column and a large brain enclosed in a skull or cranium ductus arteriosus - a blood vessel in a fetus that bypasses pulmonary circulation by connecting the pulmonary artery directly to the ascending aorta; normally closes at birth umbilical cord - membranous duct connecting the fetus with the placenta |